[unreadable] The energy expended in physical activity is an important component of energy balance and body weight. Because of the variety of physical activities that free-living humans undertake, it has been extremely challenging to obtain accurate measurements of either the amount or, energy cost of human physical activity. The energy expended in physical activity consists of energy expended in purposeful exercise and the energy expended in non-exercise activity thermogenesis (NEAT). The latter is even more difficult to measure than the former. Since most Americans engage in relatively little purposeful physical activity, the majority of energy expended in physical activity will be through NEAT. The role of NEAT in the pathophysiology of sarcopenia is poorly defined although it is widely recognized that physical activity declines with aging. The aims of this proposal are first, to ask if aging individuals indeed have decreased NEAT compared to young individuals. Second, we want to validate, in an older population, a non-invasive sensor system, the Physical Activity Monitoring System (PAMS) that measures NEAT and its components. Third, if PAMS is valid, we want to explore the components of NEAT in the elderly. Thus, we propose to address three hypotheses: Hypothesis #1: NEAT is decreased in older compared to younger non-obese, sedentary, healthy subjects. Hypothesis #2: The Physical Activity Monitoring System (PAMS) provides valid estimates of NEAT in the elderly. Hypothesis #3: Walking EE represents a lesser component of NEAT in older compared to younger nonobese, sedentary, healthy subjects. These data have the potential to help us understand the impact of aging on energy balance, nonexercise physical activity and mobility. These studies may potentially guide us to devise novel strategies to prevent sarcopenia and promote physical activity in the elderly. [unreadable] [unreadable]